Synthesis of all possible 2',3'-dideoxy-2'(3')-monofluoro and 2',3'- dideoxy-2',3'-difluoro nucleosides, including the unreported lyxo- difluoro analogue, was achieved. The same strategy will be applied to the synthesis of the corresponding thiodideoxy sugar analogues as potential anti-HIV agents. A new improved method for the synthesis of the sugar moiety of 9-(2,3- dideoxy-2-fluoro-BETA-D-threo-pentofuranosyl)adenine (FddA) - a DDN- approved compound - was completed. The aim of the method was to significantly reduce cost of production of FddA. Some refinements continue to be made. Selected acid-stable 6X-substituted-(2'-fluoro-2',3'-dideoxy-BETA-D- threo-pentofuranosyl)purines (X = F, Cl, Br, I, OMe, OEt, NHMe, NMe2, NHEt, NHNH2, NHOH, NHOMe, NHOCH2Ph, NO2) were prepared as anti-HIV adenosine deaminase-activated "pro drugs". Initial evaluation of the Cl, NHMe and OCH3 analogues showed anti-HIV activity consistent with adenosine deaminase hydrolysis rates.